232 L. V. Pirsson — Mordenite. 



thickness of 500 feet, a thickness of about 500 feet would 

 remain for the Odanah Series. 



The Laramie has nowhere been recognized in northwestern 

 Manitoba, the Cretaceous being there immediately overlain by 

 a great thickness of glacial and post-glacial deposits, and in 

 southern Manitoba the only place from which it has been 

 recorded is in Turtle Mountain,* and though the beds here 

 have since been hastily examined, their thickness has not been 

 determined. The sandstones of this terrane are associated 

 with beds of lignite that will furnish valuable local sources of 

 fuel-supply for Manitoba. 



Ottawa, May 1st, 1890. 



Aet. XXX. — On Mordenite ; by Louis Y. Pirsson. 



Under the name of mordenite in 1864, Howf published a 

 description of a new zeolite, occurring at Morden and Peter's 

 Point, Nova Scotia. To this species he assigned the general 

 formula RO, R 2 3 , (Si0 2 ) 9 6H 2 0. The correctness of this 

 formula has long been considered doubtful, owing to the high 

 ratio of silica to the bases and it is supposed that How analyzed 

 a mixture of some zeolite with silica, more especially as his 

 mineral did not occur in distinct crystals. It will therefore 

 be of interest to announce the re-discovery of this interesting 

 species in a new locality, to present a new analysis of pure 

 material, proving the correctness of How's work, together with 

 a discussion of its composition and a description of its crystal 

 form and other physical properties. 



The material upon which the present work is based I col- 

 lected in October, 1889, while engaged in temporary field work 

 on the Yellowstone Park division of the U. S. Geological Sur- 

 vey, in western Wyoming. The locality was one of the high 

 points of the ridge running eastwardly from Hoodoo Moun- 

 tain, and forming part of the divide between branches of Cran- 

 dall Creek whose waters run into Clark's Fork and the head of 

 the Lamar River or east fork of the Yellowstone. The locality 

 is several miles from Hoodoo Mountain. The mordenite 

 occurs lining the amygdaloidal cavities of a mass of decom- 

 posed basalt, one of the former inclusions in the basic breccia 

 forming the ridge. At the time it was unfortunately supposed 

 to be one of the commonly occurring zeolites and only a small 

 specimen was secured. Recently, while examining some ma- 



* Dr. Selwyn, on Boring Operations in the Souris Valley. Report of Progress, 

 G-eol. Survey of Canada, 1879-80, p. 11a. 

 f Journal of the Chemical Soc, II, ii, p. 100, 1864. 



